Numerous designs for metal shingles have been developed over the years. These shingles typically have edge flanges that are adapted to interconnect with adjacent shingles to attempt to create a substantially weather resistant barrier. Examples of such shingles are provided in U.S. Pat. No. 1,670,041 (Miller), U.S. Pat. No. 1,743,206 (Fulenwider et al.) and U.S. Pat. No. 1,876,597 (Bennett).
The Miller patent teaches a two-course shingle system where each shingle has an upper course with outwardly tapering side edges and a lower course with inwardly tapering side edges. The top, bottom and side edges of the shingle are overturned and underturned for engaging adjacent shingles. One problem with this shingle system is that shingle is subject to leakage during severe weather conditions when water may be blown upwardly to the upper course of the shingle through openings in the interlocking edges of adjacent shingles. Another problem is that the system requires close tolerances between the engaging shingles. This limits the adjustability of the shingles relative to the course below. This complicates installation when the installer is faced with obstructions such as bathroom vents, hips or valleys.
The Fulenwider patent teaches a single course shingle system where each shingle has opposing side edges that define corresponding shoulders, an underturned bottom edge and an overturned top edge. The overturned top edge is defined by a separate lock fastener that is secured to an upturned flange on the top edge of the shingle. One problem with this shingle design is that the lock fastener does not adequately seal the joint between adjacent shingles. As a result, this shingle design is subject to leakage during severe weather conditions. Another problem with the shingle system is the structure of the side shoulders. The shoulders are difficult to reproduce on site if it is necessary for an installer to cut a shingle from top to bottom to account for obstructions. As a result, installation is complicated.
The Bennett patent teaches a single course shingle system where each shingle has opposing overturned and underturned side edges and an underturned bottom edge. A separate dam strip is provided for fastening along the top edge of a course of shingles. The dam strip has a foot portion for attaching the strip to the roof, a bulge for receiving the top edge of the shingles and an angular strip that extends generally perpendicular to the roof line. One problem with this system is that the dam strip does not adequately guard against water leakage through nail holes where each shingle is attached to the roof. Also, the strip must include a cutaway portion to receive the joint at adjacent side edges. This cutaway portion is a further area where leakage can occur. Finally, the side edges have complicated contours that are difficult to reproduce on site if an installer needs to cut a shingle.
There is a need for a roofing system that overcomes the above problems. Furthermore, the roofing system should be relatively simple to install and inexpensive to manufacture.